N-(3,3-dimethylbutyl)-ATM has a sweetening potency, on the weight basis, of at least 50 times that of aspartame and about 10,000 times that of sucrose (table sugar) so that it can constitute a high intensity sweetener.
Since sweetening agents are mainly employed in foods for human consumption, they must be prepared using a method which can provide a highly purified product substantially free from impurities or decomposition products. Furthermore, in the case of a sweetener which tends to be decomposed relatively easily, like N-(3,3-dimethylbutyl)-APM, some countermeasures are required against the decomposition thereof after forwarded as a product.
The already known crystals of N-(3,3-dimethylbutyl)-APM are described in W095/30689 with reference to the IR spectrum data. The present inventors have confirmed that these crystals are monohydrate crystals as a result of X-ray-crystal structure analysis, and that they show the specific peaks of diffracted X-rays at angles of diffraction of at least 6.0°, 24.8°, 8.2° and 16.5° when measured by a powder X-ray diffractometer using CuKα radiation. The present inventors have decided to call these crystals “A-type crystal” for convenience' sake.
Meanwhile, a preparation process of N-(3,3-dimethylbutyl)-APM is also described in U.S. Pat. No. 5,278,862, wherein high purity (97% by HPLC) N-(3,3-dimethylbutyl)-APM is obtained by spontaneous crystallization using methanol and water as the crystallization solvent.
And, the present inventors have followed Example 1 of the said U.S. Pat. No. 5,278,862. As the results, although they have confirmed the reproducibility of the data on purity (98% by HPLC), they could not confirm the formation of A-type crystals. In greater detail, the N-(3,3-dimethylbutyl)-APM obtained by following the said Example 1, showed, as wet crystals, the specific peaks of diffracted X-rays at angles (2θ, CuKα rays) of diffraction of at least 5.1°, 21.1°, 21.3° and 8.3°. The powder X-ray diffraction pattern at this time will be given in FIG. 1. These crystals will hereinafter be called “B-type crystal”.
Furthermore, the B-type crystals obtained by following Example 1 of the said U.S. Pat. No. 5,728,862, when dried, gave crystals exhibiting the specific peaks of diffracted X-rays at angles (2θ, CuKα rays) of diffraction of at least 5.6°, 8.4°, 17.1° and 18.8°. The powder X-ray diffraction pattern at this time will be given in FIG. 2. As a result of measurement by the Karl Fisher's method, the water content of these crystals were found to be 0.6 wt. %. These crystals will hereinafter be called “G-type crystal”.
On the other hand, the present inventors have found that novel crystals of N-(3,3-dimethylbutyl)-APM exhibiting the specific peaks of diffracted X-rays at angles (2θ, CuKα rays) of diffraction of at least 5.4°, 8.4°, 18.8° and 17.6°, can be obtained by drying B-type crystals until their water content comes to 3 to 6 wt. %. These novel crystals will hereinafter be called “D-type crystal” for convenience' sake. The powder X-ray diffraction pattern at this time will be shown in FIG. 3.
Then, the obtained G-type crystals, D-type crystals and A-type crystals of N-(3,3-dimethylbutyl)-APM were tested at 70° C., concerning their stability. As a result, after the lapse of 271 hours, the remaining ratio of the N-(3,3-dimethylbutyl)-APM in the form of the G-type crystals and that in the form of the D-type crystals were 18 wt. % and 77 wt. %, respectively, while that in the form of the A-type crystals was 96 wt. %, suggesting that N-(3,3-dimethylbutyl)-APM is most stable in the form of A-type crystals. The relationship between the storage time and the remaining ratio of N-(3,3-dimethylbutyl)-APM in this test will be shown below in Table 1.
                   TABLE 1Stability test at 70° C.Time elapsed (hrs)0100271CrystalRemainingRemainingRemainingtypeRatio (wt. %)ratio (wt. %)Ratio (wt. %)A959496D959677G964818
As described above, it has been found that according to Example 1 of U.S. Pat. No. 5,728,862, G-type crystals of N-(3,3-dimethylbutyl)-APM which are inferior to A-type crystals in stability, are obtained.